Pressure-balancing oil system for stern tubes of ships

ABSTRACT

The oil pressure in the stern tube is maintained by the oil height in a standpipe. Valves, which are responsive to the water pressure at the level of the stern tube are arranged to automatically control the oil level in the standpipe to thereby increase or decrease the oil pressure in the stern tube and thereby maintain said pressure at a desired value above the water pressure at the level of the stern tube.

United States Patent Inventors Willis W. Gardner Waukesha; Richard L. Rafferty, Menomonee Falls, both 01 Wis.

App]. No. 5,560

Filed Jan. 26, 1970 Patented Jan. 4, 1972 Assignee Waukesha Bearings Corporation Waukesha, Wis.

PRESSURE-BALANCING OIL SYSTEM FOR STERN TUBES OF SHIPS 8 Claims, 1 Drawing Fig.

US. Cl 115/34 R, 277/3 Int. (1 B63h 5/06 Field of Search 1 15/05, 34;

[56] References Cited UNITED STATES PATENTS 3,403,915 10/1968 Roberts 277/ 3 3,176,996 4/1965 Barnett 277/3 X 3,088,744 5/1963 Ezekiel et al. 277/ 15 X Primary Examiner-Trygve M. Blix At!orney-Morse11 & Morsell ABSTRACT: The oil pressure in the stern tube is maintained by the oil height in a standpipe. Valves, which are responsive to the water pressure at the level of the stern tube are arranged to automatically control the oil level in the standpipe to thereby increase or decrease the oil pressure in the stern tube and thereby maintain said pressure at a desired value above the water pressure at the level of the stem tube.

INVENTORS WILLIS W- GARDNER RICHARD L. RAFFERTY ATTORNEYS- PRESSURE-BALANCING OIL SYSTEM FOR STERN TUBES OF SHIPS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is particularly adapted for use in the stern tube of ships, and particularly large ships such as large tankers where there can be large changes in draft.

Where there are large changes in the draft of a ship it is possible for the lubricating oil pressure in the stern tube to have a value so much in excess of the sea water pressure that there is danger of damaging the aft seals so that they do not operate properly. These seals are preferably of the radial lip type and there is a maximum pressure difference which can be handled by a sealing element of this type. If this pressure differential is exceeded, deformation of the flexible sealing elements can result. This may cause enlarged contact areas between the sealing lip and the rotating shaft. These large contact areas generate increased amounts of heat, raise the seal operating temperature, and eventually result in deterioration of the elastomer of which the seals are made. When this occurs, leakage and general seal failure result. Also, while it is customary to maintain the stern tube oil pressure at a sufficient value above sea water pressure to prevent the sea water from entering through the seals, nevertheless, due to draft changes, this may be reduced to the point where sea water can undesirably enter the stern tube.

SUMMARY OF THE INVENTION The present invention provides in a combination which includes a standpipe for maintaining a predetermined oil pressure in the stern tube, means for controlling the oil level in the standpipe to thereby increase or decrease the oil pressure in the stern tube and maintain said pressure at a desired value above sea water pressure.

A general object of the invention is to provide means for automatically maintaining the oil pressure in the stern tube at a desired value above the water pressure at the stern tube shaft level.

A further object of the invention is to provide a system as above described which includes means for sensing the differential in pressure between the oil pressure in the stern tube and the sea water pressure at the level of the stern tube, together with means responsive to the sensing mechanism for automatically maintaining the oil pressure at a desired value above the sea water pressure.

A more specific object of the present invention is to provide a standpipe for maintaining a predetermined oil pressure in the stern tube, together with means including a first valve, responsive to an increased water pressure for raising the elevation of the oil in the standpipe to thereby increase the oil pressure in the stern tube, and means including a second valve, responsive to a decrease in water pressure, for lowering the level of the oil in the standpipe to decrease pressure in the stern tube, whereby the desired difference in oil pressure over water pressure may be reestablished.

A further object of the invention is to provide a system as above described which is relatively simple and foolproof in operation in that the oil pressure in the stern tube is normally maintained by the level of oil in a standpipe, there being an hydraulic circuit including a circulating pump for normally circulating the oil through the stern tube, which pump is also employed in the present novel system to lower the height of the oil in the standpipe when this becomes necessary.

A further object of the invention is to provide a system as above described which increases the effectiveness and life of the aft seals.

With the above and other objects in view, the invention consists of the improved pressure-balancing oil system for stem tubes of ships, and all of its parts and combinations, as set forth in the claims, and all equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, the FIGURE is a partially diagrammatic view showing the improved system, part of the stern tube being broken away and shown in longitudinal section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawing, the numeral 10 designates a stern tube having a forward bearing 11 and an aft bearing 12 through which the tail shaft 13 is joumaled, the tail shaft carrying the usual propeller 14 for a ship 15. Between the aft bearing 12 and the propeller 14 is the housing 16 for the aft sealing assembly, which assembly includes seals of any conventional type, but which are preferably of the radial lip type of elastomeric material and are designed to retain the oil within the stern tube and to resist entrance of sea water into the stern tube. Forwardly of the forward bearing 11 is the housing 17 for a forward seal assembly. This assembly may include seals of any conventional type, but preferably radial-liptype seals of elastomeric material.

Lubricating oil from a sump tank 18 is adapted to be circulated by a pump 19 driven by a motor 20 past an orifice 21 through a conduit 22 to an aft portion of the stern tube. A return line 23 for oil from the stern tube may extend from a forward portion of the stern tube to the sump. A standpipe 24 communicates with the oil chamber 9 within the stern tube, and the head of oil in the standpipe is adapted to maintain a desired oil pressure in the stern tube as will be hereinafter described. This level in the standpipe is indicated by L in the drawing. The standpipe has a downwardly hooked upper end 25 extending into the top of an oil reservoir 26. Conduit 27 connects the bottom of the oil reservoir with the junction 28 between the pump discharge conduit 22 and the conduit 22 leading to the stern tube.

Positioned at the level S of the stern tube axis is the inlet end 29 of a draft-sensing conduit 30, which inlet is positioned to sense the water pressure at the shaft level S. The draft-sensing conduit 30 is used in conjunction with additional means for sensing the differential pressure between the oil pressure in the stern tube chamber and the sea water pressure at 29,

which mechanism is arranged to automatically maintain the oil pressure in the stern tube at a desired value above the sea water pressure at 29. While various types of valves or other control instrumentalities may be used to accomplish the above purpose, in the preferred embodiment illustrated the sensing line 30 is connected by a branch conduit 31 with the left-hand side of a diaphragm valve 32, there being a stem 33 connected to a valve member 34 which is moved to the right in response to an increase in pressure in the line 31 to open the valve 34. Spring 33 normally urges the valve 34 to closing position.

The sensing conduit 30 is also connected by a branch 35 with the right-hand side of another diaphragm valve 36. The diaphragm valve 36 includes a projecting stem 37 carrying a valve member 38 which controls flow through the line 27. Spring 37 normally urges the valve 38 to closing position. A conduit 39 connects the left-hand side of the diaphragm valve 36 with the right-hand side of the diaphragm valve 32, and with the sump conduit 40. The sump conduit 40 serves to allow the oil pressure in the stern tube system to act on both diaphragm valves 32 and 36 so that the valves are capable of being responsive to the pressure differential between the oil pressure in the stern tube and the sea water pressure at 29. The diaphragm valve 36, without the spring 37 would nor mally be urged to open position by the pressure from the lines 40-39. The spring 37', however, is set to normally urge the valve to closed position. Valve 34 would normally be closed regardless of the spring 33. Therefore, the springs 37' and 33' are set differently to accomplish the desired purpose of normally maintaining both valves closed for a small range of pressure difference.

OPERATION Normally the level L in the standpipe 24 will maintain the oil pressure in the stern tube at a fixed value above sea water pressure. lf, however, due to an increase in the draft of the ship, the sea water pressure increases, this will be sensed by the sensing conduit 30 and valve 32 will be opened allowing oil from the reservoir 26 to enter the system through the conduit 40 leading to the sump. This increase in the amount of oil in the system will raise the height of the oil level L in the stand pipe to increase the oil pressure in the stern tube a sufficient amount to reestablish the desired differential between the stern tube oil pressure and the water pressure at the level of the tail shaft. When this difference has been reestablished the valve 32 will automatically close.

If the water pressure at tail shaft level S decreases due to a lessening of the draft of the ship, valve 36 will be opened allowing oil to be pumped from the stern tube to the reservoir 26. This opening of valve 38 is due to the pump pressure in conduit 40-39, which is now greater than the lowered pressure on the right-hand side of valve 36 plus the action of spring 37. This opening of valve 38 lowers the oil level L in the standpipe and thus lowers the oil pressure in the stern tube. When this pressure in the stern tube has decreased sufficiently to reestablish the required difference between stern tube pressure and water pressure the valve 36 will close. As before mentioned, the springs 37 and 33' for the valves 36 and 32 are set to provide for a small range of pressure difference during which both valves remain closed.

It is to be noted that the pressure in the stern tube is normally maintained by the head of oil in the standpipe, the pump 19 being used only for circulation of oil through the stern tube and to lower the height of oil in the standpipe when this is required. The orifice 21 is used to establish a discharge pressure from the pump 19 sufficient to allow oil to be pumped up into reservoir 26 when valve 36 opens. The reservoir 26 is vented to atmosphere as at 41.

lt is to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

What is claimed is:

1. In a ship having a stern tube with an oil chamber therein containing oil, a standpipe communicating with said oil chamber and having oil at a predetermined level for maintaining a predetermined head pressure on the oil in the stern tube, means including an hydraulic circuit for circulating oil through said oil chamber, and means responsive to changes in the draft of the ship for varying the oil level in the standpipe to thereby vary the head pressure in the stern tube and maintain it at a predeterminedvalue.

2. A pressure-balancing oil system as claimed in claim 1 in which the means which is responsive to changes in the draft of the ship is responsive to water pressure at the level of the stern tube.

3. A pressure-balancing oil system as claimed in claim 1 in which the means which is responsive to changes in the draft of the ship includes means responsive to an increase in water pressure at the level of the stern tube for increasing the height of the oil in the standpipe, and means responsive to a decrease in water pressure at the level of the stern tube for decreasing the height of the oil in the standpipe.

4. A pressure-balancing oil system as claimed in claim 1 in which there is an oil reservoir, and in which the means which is responsive to changes in the draft of the ship for varying the oil level in the standpipe includes mechanism which is responsive to an increase in water pressure at the level of the stern tube for adding oil from the reservoir to the stern tube hydraulic circuit to thereby increase the oil level in the standpipe, and which is responsive to a decrease in the water pressure at the level of the stern tube for returning oil from the stern tube hydraulic circuit to the reservoir to decrease the oil level in the standpipe.

5. A pressure-balancing oil system as claimed in claim 4 in which said mechanism includes two valves, one of which controls the flow of oil from the reservoir to the stern tube hydraulic circuit and is opened in response to an increase in water pressure at the level of the stern tube to open the valve, and the other of which controls the flow of oil to the reservoir and is opened in response to a decrease in water pressure at the level of the stern tube.

6. In a ship having a stern tube with an oil chamber therein containing oil, a standpipe communicating with said oil chamber and having oil at a predetermined level for maintaining a predetermined head pressure, means including an hydraulic circuit having a sump and having a pump for circulating oil through said oil chamber, an elevated oil reservoir, a conduit between said reservoir and said hydraulic circuit, a normally closed valve normally preventing the pumping of oil from said hydraulic circuit to the reservoir, a conduit connecting the oil reservoir with the sump, a normally closed valve normally preventing the flow of oil from the reservoir to the sump, and means responsive to water pressure at the level of the stern tube for causing opening of said second mentioned valve when there is an increase in water pressure and for causing opening of said first-mentioned valve when there is a decrease in water pressure to thereby automatically maintain the oil pressure in the stern tube chamber at a predetermined value above water pressure.

7. A pressure-balancing oil system for stern tubes of ships as claimed in claim 6 in which the valves are diaphragm-operated and include a pressure chamber on each side of the diaphragm and in which the means which is responsive to water pressure is connected to a first pressure chamber of the first-mentioned diaphragm-operated valve and to the opposite pressure chamber of the second-mentioned diaphragm-operated valve, and in which the other pressure chamber of the first-mentioned diaphragm-operated valve and the other pressure chamber of the second-mentioned diaphragm-operated valve are both connected to the hydraulic circuit to be subjected to the pressure therein.

8. In a ship having a stern tube with an oil chamber therein, means for normally maintaining a predetermined pressure on the oil in said chamber, and means responsive to changes in the draft of the ship for varying the oil pressure in the oil chamber to maintain it at a predetermined value, said last means including a pair of valves, one of which is continuously responsive to water pressure at the level of the stern tube to increase oil pressure in the stern tube oil chamber by a sufiicient amount, when required, to reestablish the desired differential between the stern tube chamber oil pressure and said water pressure, and the other of which is continuously responsive to water pressure at the level of the stern tube to decrease the oil pressure in the stern tube chamber by a sufficient amount, when required, to reestablish the desired differential between the stern tube chamber oil pressure and said water pressure. 

1. In a ship having a stern tube with an oil chamber therein containing oil, a standpipe communicating with said oil chamber and having oil at a predetermined level for maintaining a predetermined head pressure on the oil in the stern tube, means including an hydraulic circuit for circulating oil through said oil chamber, and means responsive to changes in the draft of the ship for varying the oil level in the standpipe to thereby vary the head pressure in the stern tube and maintain it at a predetermined value.
 2. A pressure-balancing oil system as claimed in claim 1 in which the means which is responsive to changes in the draft of the ship is responsive to water pressure at the level of the stern tube.
 3. A pressure-balancing oil system as claimed in claim 1 in which the means which is responsive to changes in tHe draft of the ship includes means responsive to an increase in water pressure at the level of the stern tube for increasing the height of the oil in the standpipe, and means responsive to a decrease in water pressure at the level of the stern tube for decreasing the height of the oil in the standpipe.
 4. A pressure-balancing oil system as claimed in claim 1 in which there is an oil reservoir, and in which the means which is responsive to changes in the draft of the ship for varying the oil level in the standpipe includes mechanism which is responsive to an increase in water pressure at the level of the stern tube for adding oil from the reservoir to the stern tube hydraulic circuit to thereby increase the oil level in the standpipe, and which is responsive to a decrease in the water pressure at the level of the stern tube for returning oil from the stern tube hydraulic circuit to the reservoir to decrease the oil level in the standpipe.
 5. A pressure-balancing oil system as claimed in claim 4 in which said mechanism includes two valves, one of which controls the flow of oil from the reservoir to the stern tube hydraulic circuit and is opened in response to an increase in water pressure at the level of the stern tube to open the valve, and the other of which controls the flow of oil to the reservoir and is opened in response to a decrease in water pressure at the level of the stern tube.
 6. In a ship having a stern tube with an oil chamber therein containing oil, a standpipe communicating with said oil chamber and having oil at a predetermined level for maintaining a predetermined head pressure, means including an hydraulic circuit having a sump and having a pump for circulating oil through said oil chamber, an elevated oil reservoir, a conduit between said reservoir and said hydraulic circuit, a normally closed valve normally preventing the pumping of oil from said hydraulic circuit to the reservoir, a conduit connecting the oil reservoir with the sump, a normally closed valve normally preventing the flow of oil from the reservoir to the sump, and means responsive to water pressure at the level of the stern tube for causing opening of said second mentioned valve when there is an increase in water pressure and for causing opening of said first-mentioned valve when there is a decrease in water pressure to thereby automatically maintain the oil pressure in the stern tube chamber at a predetermined value above water pressure.
 7. A pressure-balancing oil system for stern tubes of ships as claimed in claim 6 in which the valves are diaphragm-operated and include a pressure chamber on each side of the diaphragm and in which the means which is responsive to water pressure is connected to a first pressure chamber of the first-mentioned diaphragm-operated valve and to the opposite pressure chamber of the second-mentioned diaphragm-operated valve, and in which the other pressure chamber of the first-mentioned diaphragm-operated valve and the other pressure chamber of the second-mentioned diaphragm-operated valve are both connected to the hydraulic circuit to be subjected to the pressure therein.
 8. In a ship having a stern tube with an oil chamber therein, means for normally maintaining a predetermined pressure on the oil in said chamber, and means responsive to changes in the draft of the ship for varying the oil pressure in the oil chamber to maintain it at a predetermined value, said last means including a pair of valves, one of which is continuously responsive to water pressure at the level of the stern tube to increase oil pressure in the stern tube oil chamber by a sufficient amount, when required, to reestablish the desired differential between the stern tube chamber oil pressure and said water pressure, and the other of which is continuously responsive to water pressure at the level of the stern tube to decrease the oil pressure in the stern tube chamber by a sufficient amount, when required, to reestablish the desired differential between the stern tube chambeR oil pressure and said water pressure. 